Plankton (zoo- and
phytoplankton) samples were collected with the aid
of a plankton net (mesh size: 55 μm) through vertical
hauls from the upper layer of 10 cm. Filtered plankton
samples were acidified with HCl and kept for analysis.
Parts of gills, skin, and dorsal muscle were taken from
each fish, weighed, put in small Erlenmeyer flasks,
dried in an oven at 105 °C for about 24 h, and acid-